The present invention relates to subterranean treatment operations, and more particularly, to providing controlled delivery of subterranean fluid additives to a well bore treatment fluid and/or a surrounding subterranean environment using intelligent materials that respond to a magnetic stimulus to release subterranean fluid additives downhole in a subterranean environment.
Natural resources such as oil and gas located in a subterranean formation can be recovered by drilling a well bore in the subterranean formation, typically while circulating a drilling fluid in the well bore. After the well bore is drilled, a string of pipe, e.g., casing, can be run in the well bore. The drilling fluid is then circulated downwardly through the interior of the pipe and upwardly through the annulus between the exterior of the pipe and the walls of the well bore, although other methodologies are known in the art.
Hydraulic cement compositions are commonly employed in the drilling, completion and repair of oil and gas wells. For example, hydraulic cement compositions are utilized in primary cementing operations whereby strings of pipe such as casing or liners are cemented into well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a pipe string disposed therein. The cement composition is allowed to set in the annular space, thus forming an annular sheath of hardened substantially impermeable cement. This cement sheath physically supports and positions the pipe string relative to the walls of the well bore and bonds the exterior surfaces of the pipe string to the walls of the well bore. The cement sheath prevents the unwanted migration of fluids between zones or formations penetrated by the well bore.
Hydraulic cement compositions are also commonly used to plug lost circulation and other undesirable fluid inflow and outflow zones in wells, to plug cracks and holes in pipe strings cemented therein and to accomplish other required remedial well operations.
After the cement is placed within the well bore a period of time is needed for the cement to cure and obtain enough mechanical strength for drilling operations to resume. This down time is often referred to as “waiting-on-cement.” If operations are resumed prior to the cement obtaining sufficient mechanical strength, the structural integrity of the cement can be compromised.
In carrying out primary cementing as well as remedial cementing operations in well bores, the cement compositions are often subjected to high temperatures, particularly when the cementing is carried out in deep subterranean zones. These high temperatures can shorten the thickening times of the cement compositions, meaning the setting of the cement takes place before the cement is adequately pumped into the annular space. Therefore, the use of set retarding additives in the cement compositions has been required. These additives extend the setting times of the compositions so that adequate pumping time is provided in which to place the cement into the desired location.
A variety of cement set retarding additives have been developed and are utilized in oil well cementing, such as sugars or sugar acids. Hydroxy carboxylic acids, such as tartaric acid, gluconic acid and glucoheptonic acid are also commonly used in oil well cementing as retarders. However, if an excess amount of retarder is used it can over-retard the set of the cement slurry, thereby causing it to remain fluid for an extended period of time. This over-retardation can result in an extended waiting-on-cement time and cause delays in subsequent drilling or completion activities.
In a number of cementing applications, aqueous salts have been utilized as an additive in cement compositions. Certain salts, such as calcium salts, can act as accelerating agents, which reduce the setting time of the cement composition in an attempt to overcome the negative effects of set retarders. However, the presence of a set and strength accelerating agent, such as calcium salt, in the cement composition can increase the risk that the cement composition may thicken or set before placement.
Given the complexity of the cement chemistry and the large temperature and pressure gradients present in the well bore, and the difficulty in predicting the exact downhole temperatures during the placement and setting of the cement, it can be difficult to control the retarding additive and accelerating agent to get the desired setting behavior. There is a need for improved set control methods, which bring about predictable cement composition setting times in the subterranean environments encountered in wells. In particular, it is desirable to develop methods for rapidly setting cement-based systems whereby the timing of the setting is under the control of technicians in the field without the risk of premature setting. Therefore, a cement that can be made to set on demand within the well bore is desirable. Such cement compositions could be useful, for example, when lost circulation zones are encountered in the subterranean formation. Setting a cement composition on demand to seal off the leak to the lost circulation zone would be desirable.
Other subterranean fluids can also benefit from the initiation of a chemical reaction downhole on demand. For example, it may be desirable to have a fluid that comprises a polymer crosslink downhole to form a pill to counteract lost circulation. The fluid could require less hydrostatic pressure for pumping, and then crosslink downhole when and where desired to form a more viscous fluid that may prevent fluid loss. Other downhole fluids and chemicals may also benefit from the ability to be activated on demand within a subterranean formation.